Gordon Glover over at Beyond the Firmament has an excellent discussion on the old creationism stand-by, appearance of age. He writes:
Consider the Garden of Eden on the day God rested from His work. If we understand the narrative as a historical account, the universe would have been fully functional. Light from distant stars was already reaching Earth. Large trees with their many annual rings populated the Garden. Mountains and valleys appeared weathered by erosion. Adam and Eve presumably spoke a human language with rules and conventions already learned and rehearsed. Adam appeared to have some experience with horticulture and animal husbandry, and Eve appeared to have some domestic skills. Millions of different species each filled their ecological niches as if they had been doing so for ages.
He is quite correct. If everything were created in six days, some appearance of age would be unavoidable. To me, though, the biggest stumbling block in the whole appearance of age thing is that the YEC crowd tries to have it both ways. First, they try to show that the earth shows signs of being created in six days (for example, the RATE Project, The Grand Canyon Research Project), then, when it doesn't, it reflects the appearance of age. Uh, sorry. That doesn't work. If it shows the appearance of age, then it should show the appearance of age EVERYWHERE. If it doesn't, then it means that God screwed up in places when He was going around artificially aging things. As I have written before, this becomes a Time Bandits God, not the God we know from the Bible.